Stephanie is 3 times as old as Omar and is also 10 years older than Omar. How old is Omar?
Explanation: We can use the given information to write down two equations that describe the ages of Stephanie and Omar. Let Stephanie's current age be $s$ and Omar's current age be $o$ $s = 3o$ $s = o + 10$ Now we have two independent equations, and we can solve for our two unknowns. Since we are looking for $o$ , and both of our equations have $s$ alone on one side, this is a convenient time to use elimination. Subtracting the second equation from the first equation, we get: $0 =$ $3o$ $-$ $ (o + 10)$ which combines the information about $o$ from both of our original equations. Solving for $o$ , we get: $2 o = 10$ $o = 5$.